Subsea hydrocarbon exploration and production presents enormous challenges to operators. The combination of high temperature and high pressures that oilfield equipment has to withstand requires a high degree of testing and qualification. Drilling and production equipment, including casing, wellheads, risers, connections, and other associated equipment must be designed to sustain high load conditions. These conditions are compounded by the fact that offshore oilfield operations are not on a stable platform compared to a land-based oilfield operation. For instance, the wave induced motion of an offshore deepwater rig causes bending moments in the tubing that would not otherwise occur on a stationary land rig. As a result, these stresses and bending moments must be considered when designing and testing tubulars for offshore operations.
Tubulars used offshore experience higher than normal loads in terms of magnitude and non-normal orientations. For instance, when a tubular is connected from a wellhead to a drilling ship over a vertical distance of hundreds or thousands of feet, even a small movement of the drilling ship relative to the wellhead can cause enormous bending in the tubular.
Facilities and test beds for testing land based equipment does not produce the stresses seen offshore. The loads seen in subsea oilfield equipment are often several times to several orders of magnitude higher than land operations. As a result, testing and verifying the strength of the equipment is more difficult.
Load frames suitable for subsea oilfield equipment testing are large and expensive. Conventional frame designs are often configured to apply primary tension loadings. These frame designs typically include two or more structural members in parallel to the test sample. The two or more structural members are connected to platen ends. The test sample is then loaded typically by one or more hydraulic cylinders.
These hydraulic cylinders apply a tension force to the sample, however other loads can be applied as well. For instance, a bending load can be applied by a hydraulic cylinder loading from the side. Combined tension and bending loading can also be applied. The problem with the typical design is that the tension and bending loads must be contained within the test structure itself. The test structure must be sufficiently strong such that it too does not deform significantly in response to the loads applied to the test sample. As a result, simply increasing the test load capacity of a test structure using more powerful cylinders can cause the test structure to become too large and too expensive.
An example of current designs includes a sample test article, such as a tubular, bolted perpendicular to two beams to form a “H pattern” setup. Two hydraulic cylinders are connected to both beams and lined up parallel with the sample test article. The hydraulic cylinders can be pressurized the same amount to apply an axial load, or they can apply different forces to induce a moment in the test article. To test ever larger loads however requires larger hydraulic cylinders, driving up the costs. Moreover, in this setup the test article is in part supporting the test structure because the hydraulic cylinders are typically connected to the beams via pins. This allows unwanted forces in the test article during testing.
Furthermore, hydraulic cylinders are precision devices that also increase exponentially in cost as the size increases. There is a point where the cylinders themselves become too large and too expensive to test samples beyond a certain point. As a result, there exists a need to develop a test bed for subsea equipment that does not rely on ever increasing test structures and hydraulic cylinders.